CVE-2026-45910

In the Linux kernel, the following vulnerability has been resolved:

RDMA/rxe: Fix race condition in QP timer handlers

I encontered the following warning: WARNING: drivers/infiniband/sw/rxe/rxe_task.c:249 at rxe_sched_task+0x1c8/0x238 [rdma_rxe], CPU#0: swapper/0/0 … libsha1 [last unloaded: ip6_udp_tunnel] CPU: 0 UID: 0 PID: 0 Comm: swapper/0 Tainted: G C 6.19.0-rc5-64k-v8+ #37 PREEMPT Tainted: [C]=CRAP Hardware name: Raspberry Pi 4 Model B Rev 1.2 Call trace: rxe_sched_task+0x1c8/0x238 [rdma_rxe] (P) retransmit_timer+0x130/0x188 [rdma_rxe] call_timer_fn+0x68/0x4d0 __run_timers+0x630/0x888 … WARNING: drivers/infiniband/sw/rxe/rxe_task.c:38 at rxe_sched_task+0x1c0/0x238 [rdma_rxe], CPU#0: swapper/0/0 … WARNING: drivers/infiniband/sw/rxe/rxe_task.c:111 at do_work+0x488/0x5c8 [rdma_rxe], CPU#3: kworker/u17:4/93400 … refcount_t: underflow; use-after-free. WARNING: lib/refcount.c:28 at refcount_warn_saturate+0x138/0x1a0, CPU#3: kworker/u17:4/93400

The issue is caused by a race condition between retransmit_timer() and rxe_destroy_qp, leading to the Queue Pairs (QP) reference count dropping to zero during timer handler execution.

It seems this warning is harmless because rxe_qp_do_cleanup() will flush all pending timers and requests.

Example of flow causing the issue:

CPU0 CPU1 retransmit_timer() { spin_lock_irqsave rxe_destroy_qp() __rxe_cleanup() __rxe_put() // qp->ref_count decrease to 0 rxe_qp_do_cleanup() { if (qp->valid) { rxe_sched_task() { WARN_ON(rxe_read(task->qp) <= 0); } } spin_unlock_irqrestore } spin_lock_irqsave qp->valid = 0 spin_unlock_irqrestore }

Ensure the QPs reference count is maintained and its validity is checked within the timer callbacks by adding calls to rxe_get(qp) and corresponding rxe_put(qp) after use.

Weakness

The product contains a concurrent code sequence that requires temporary, exclusive access to a shared resource, but a timing window exists in which the shared resource can be modified by another code sequence operating concurrently.

Affected Software

Extended Description

A race condition occurs within concurrent environments, and it is effectively a property of a code sequence. Depending on the context, a code sequence may be in the form of a function call, a small number of instructions, a series of program invocations, etc. A race condition violates these properties, which are closely related:

A race condition exists when an “interfering code sequence” can still access the shared resource, violating exclusivity. The interfering code sequence could be “trusted” or “untrusted.” A trusted interfering code sequence occurs within the product; it cannot be modified by the attacker, and it can only be invoked indirectly. An untrusted interfering code sequence can be authored directly by the attacker, and typically it is external to the vulnerable product.

Potential Mitigations

• Minimize the usage of shared resources in order to remove as much complexity as possible from the control flow and to reduce the likelihood of unexpected conditions occurring.
• Additionally, this will minimize the amount of synchronization necessary and may even help to reduce the likelihood of a denial of service where an attacker may be able to repeatedly trigger a critical section (CWE-400).

Related Attack Patterns

• https://cwe.mitre.org/data/definitions/26.html
• https://cwe.mitre.org/data/definitions/29.html

References

• https://git.kernel.org/stable/c/3c2ae79fb19dfd67341c14f1e78a5f1744eacfe2
• https://git.kernel.org/stable/c/5ae9da022ee3c97e6469eabcddce9271501ddbad
• https://git.kernel.org/stable/c/756c93d6df7c3bc599f6590b8e5afead6a41de1c
• https://git.kernel.org/stable/c/87bf646921430e303176edc4eb07c30160361b73
• https://git.kernel.org/stable/c/da379ca16af3722f159860d91a99cb6976a7500f